Numerous compositions for lubricating aluminum alloy materials are known in the prior art. However, there is still a need for aluminum alloy finstock material which is prelubricated before use and which also has good lubricity, cleanability and wettability properties. The term "lubricity" means the ability of a lubricant to maintain its film strength after aging and also after coming into contact with water. "Cleanability" means the ability to easily remove the lubricant from the finstock surface, preferably by rinsing with water. "Wettability" means the ability to cause spreading of water droplets as measured by contact angle.
At the present time, most aluminum alloy finstock is lubricated with oil at the time of shaping in a fin press die. Consequently, the shaped fins must be degreased after being formed into fins. Degreasing requires usage of an organic solvent such as trichlorethylene, which itself poses hazards to the health and safety of workers, as well as increased handling and transportation costs in disposal to assure the avoidance of environmental pollution.
Proposals have been made to reduce the problems noted above by lubrication with a lubricating oil dissolved in a volatile solvent. After the finstock is shaped into fins, the solvent evaporates, leaving residual oil on surface portions of the fins. Such residual oil is difficult to remove other than with volatile solvents and, if left on the fins, provides a hydrophobic surface which interferes with efficient operation of the fins. The evaporated solvents may also cause unacceptable emission problems.
Several processes for producing hydrophilic coatings on aluminum alloy finstock are known in the prior art. Some references disclosing hydrophilic finstock coatings are Kaneko et al U.S. Pat. No. 4,421,789; Uchiyama et al U.S. Pat. No. 4,462,842; Imai et al U.S. Pat. No. 4,588,025; Kaneko et al U.S. Pat. No. 4,726,886; Sako et al U.S. Pat. Nos. 4,783,224 and 4,954,372; Mizoguchi et al U.S. Pat. No. 4,957,159; and Yamasoe U.S. Pat. No. 4,973,359. These finstock coatings perform satisfactorily in preventing accumulations of water droplets which might increase resistance to air flow adjacent the fins and thereby reduce heat exchange efficiency. However, it has been found that coated finstock also increases wear rates on forming dies which shape the finstock into heat exchanger fins. Attempts to reduce wear on the forming dies by lubrication with a conventional oil-base lubricant result in a need to degrease the shaped fins so that they may benefit from their hydrophilic coating. Accordingly, there is a need for a suitable lubricant composition which will reduce wear rates on the forming dies to satisfactory levels.
Courval U.S. Pat. No. 4,928,508 has proposed lubricating hydrophilic aluminum alloy finstock with a water-soluble lubricant coating that is dried before shipping and storage. The preferred water-soluble lubricant is an ethoxylated castor oil having some solubility in water. However, because of the limited solubility of ethoxylated castor oil in water, cleanability of fins made from the finstock may not be assured. In addition, the Courval lubricant composition is dissolved in isopropanol for application to the finstock. Health and safety concerns require specialized procedures and equipment in the use of isopropanol and other alcoholic solvents with consequent increased costs.